This section provides background information related to the present disclosure which is not necessarily prior art.
An internal combustion engine typically employs camshaft(s) to open and close the engine's valves in order to control a supply of intake air to the cylinder for combustion therein and removal of post-combustion gas therefrom. A camshaft-drive element, such as a timing belt or a timing chain, is frequently used to synchronize the rotation of an engine's crankshaft and camshaft(s) so that the engine's intake and exhaust valves open and close at proper times during each cylinder's intake and exhaust strokes.
A tensioner is frequently used in an engine with either the timing belt or chain. Such a tensioner generally applies a force to the timing belt or chain to maintain the belt or chain in tension and, therefore, the rotational timing between the engine's crankshaft and camshaft(s). The tensioner ensures that, independent of the motion of the belt or chain, the connection between the engine's crankshaft and camshaft(s) remains intact, while limiting stress on the related components.
Current tensioners have a spring within them to load the cam drive system with enough load to control the cam timing at start (low engine speeds) and at high engine speeds. But in the midrange of engine speeds a much lower spring force is required. Accordingly, the present disclosure supplies oil pressure to work against the spring load so at the midrange engine speeds (generally 1000-3000 RPM) a much lower cam drive tension is achieved. By reducing the tension on the drive element at midrange speeds, a reduction in friction can be achieved. Such a friction reduction can result in a fuel economy improvement. In addition, the resultant lower average tension on the cam drive also increases component reliability.
Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.